allow qemu_iovec_from_buffer() to specify offset from which to start copying

Similar to
 qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
                   int c, size_t bytes);
the new prototype is:
 qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
                     const void *buf, size_t bytes);

The processing starts at offset bytes within qiov.

This way, we may copy a bounce buffer directly to
a middle of qiov.

This is exactly the same function as iov_from_buf() from
iov.c, so use the existing implementation and rename it
to qemu_iovec_from_buf() to be shorter and to match the
utility function.

As with utility implementation, we now assert that the
offset is inside actual iovec.  Nothing changed for
current callers, because `offset' parameter is new.

While at it, stop using "bounce-qiov" in block/qcow2.c
and copy decrypted data directly from cluster_data
instead of recreating a temp qiov for doing that.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

4 files changed, 8 insertions, 11 deletions

diff --git a/block/curl.c b/block/curl.c
index bf3680b..e7c3634 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -140,8 +140,8 @@ static size_t curl_read_cb(void *ptr, size_t size, size_t nmemb, void *opaque)
             continue;
 
         if ((s->buf_off >= acb->end)) {
-            qemu_iovec_from_buffer(acb->qiov, s->orig_buf + acb->start,
-                                   acb->end - acb->start);
+            qemu_iovec_from_buf(acb->qiov, 0, s->orig_buf + acb->start,
+                                acb->end - acb->start);
             acb->common.cb(acb->common.opaque, 0);
             qemu_aio_release(acb);
             s->acb[i] = NULL;
@@ -176,7 +176,7 @@ static int curl_find_buf(BDRVCURLState *s, size_t start, size_t len,
         {
             char *buf = state->orig_buf + (start - state->buf_start);
 
-            qemu_iovec_from_buffer(acb->qiov, buf, len);
+            qemu_iovec_from_buf(acb->qiov, 0, buf, len);
             acb->common.cb(acb->common.opaque, 0);
 
             return FIND_RET_OK;
diff --git a/block/qcow.c b/block/qcow.c
index 35dff49..7280103 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -540,7 +540,7 @@ done:
     qemu_co_mutex_unlock(&s->lock);
 
     if (qiov->niov > 1) {
-        qemu_iovec_from_buffer(qiov, orig_buf, qiov->size);
+        qemu_iovec_from_buf(qiov, 0, orig_buf, qiov->size);
         qemu_vfree(orig_buf);
     }
 
diff --git a/block/qcow2.c b/block/qcow2.c
index fcbf952..ccc599b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -590,7 +590,7 @@ static coroutine_fn int qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,
                 goto fail;
             }
 
-            qemu_iovec_from_buffer(&hd_qiov,
+            qemu_iovec_from_buf(&hd_qiov, 0,
                 s->cluster_cache + index_in_cluster * 512,
                 512 * cur_nr_sectors);
             break;
@@ -630,11 +630,8 @@ static coroutine_fn int qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,
             if (s->crypt_method) {
                 qcow2_encrypt_sectors(s, sector_num,  cluster_data,
                     cluster_data, cur_nr_sectors, 0, &s->aes_decrypt_key);
-                qemu_iovec_reset(&hd_qiov);
-                qemu_iovec_copy(&hd_qiov, qiov, bytes_done,
-                    cur_nr_sectors * 512);
-                qemu_iovec_from_buffer(&hd_qiov, cluster_data,
-                    512 * cur_nr_sectors);
+                qemu_iovec_from_buf(qiov, bytes_done,
+                    cluster_data, 512 * cur_nr_sectors);
             }
             break;
 
diff --git a/block/rbd.c b/block/rbd.c
index 1280d66..8bb3252 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -620,7 +620,7 @@ static void rbd_aio_bh_cb(void *opaque)
     RBDAIOCB *acb = opaque;
 
     if (acb->cmd == RBD_AIO_READ) {
-        qemu_iovec_from_buffer(acb->qiov, acb->bounce, acb->qiov->size);
+        qemu_iovec_from_buf(acb->qiov, 0, acb->bounce, acb->qiov->size);
     }
     qemu_vfree(acb->bounce);
     acb->common.cb(acb->common.opaque, (acb->ret > 0 ? 0 : acb->ret));